Dental materials such as for example, dental filling materials, often include liquid polymerizable organic monomers and/or polymers, reactive diluents, polymerization initiators, stabilizers, and fillers. Such composite materials have their good mechanical properties such as high flexural strengths, high compressive strengths and hardness. Further, they are often polishable and readily accept suitable dyes. The most frequently used monomers are esters of methacrylates and higher multifunctional alcohols or isocyanates such as the bismethacrylate of biphenol-A diglycidyl ether, urethane bismethacrylates. Aromatic dials are often used to make polymerizable resins having good thermal and mechanical stability.
Bisphenol A (BPA) has been widely used in the manufacture of plastics and is present in many products, including dental products. Both the U.S. Food and Drug Administration and the National Toxicology Program at the National Institute of Health have expressed concern about the potential health effects associated with BPA.
Although BPA is not an ingredient in any dental products, it has been detected in some of the degraded dental products that contain BPA-based dental resins. BisGMA is one such BPA-based dental resin and has been widely used in many dental products. Regardless of the debate over the effect of potentially leached BPA from cured dental products that contain BisGMA or its derivatives, there are increasing efforts to manufacture BPA-free resins.
BisGMA is a high viscosity, dimethacrylate resin. Various structural modifications on BisGMA have been made in order to reduce its viscosity and to minimize the polymerization shrinkage and curing stress. The rigid aromatic moiety in BisGMA does contribute well to the high strength in cured BisGMA and its derivatives, although they are usually accompanied by higher shrinkage and higher curing stress. Conventional aliphatic resins, such as TEGDMA or UDMA are flexible and have low viscosity but they usually offer lower mechanical property. A variety of cyclic aliphatic moieties were also incorporated into polymerizable resins and an improved chemical property was demonstrated due to the rigid nature. However, most of monomer resins containing cyclic moiety are highly crystalline due to its chain regularity, which would limit its application as matrix resin for formulated dental composites. Therefore oligomeric resins have to be prepared, but these amorphous resins tend to have higher viscosity. Accordingly there is reduced cross-linking density after curing and furthermore lower mechanical property would result.
Bisphenol A (BPA) in particular is one such aromatic diol that has been widely used in epoxy resin, modified methacrylate resin, polyethersulfone/ketone, polyester, polycarbonate and the like, for use in dental materials. Resins or polymers from fully aliphatic diols are less popular due to their relative lower thermal stability. However, there have been investigations of resins and polymers based on cyclic aliphatic compounds, especially those that are multi-cyclic. Interest in such cyclic aliphatic dials has increased due to potential concerns of some aromatic diol, especially BPA. Accordingly, BPA-free resins or polymers would be highly desirable if they possessed the same or comparable thermal and mechanical stabilities as the BPA counterparts.